The fundamental objectives of the proposed program are to gain an understanding of the mechanisms by which cellular functions are regulated by protein phosphorylation and to elaborate on the role of protein phosphorylation as the mechanism of action of cAMP. In each area the control of glycogen metabolism will serve as a model system. We propose an investigation of the phosphorylation of phosphorylase kinase and glycogen synthase in the perfused rat heart so that we may identify and distinguish control processes mediated by cAMP and those otherwise regulated. That investigation is necessarily coordinated with the purification and physico-chemical characterization of cardiac phosphorylase kinase and glycogen synthase. These data will be correlated with studies of the isolated enzymes from the same tissues.